Discussion on some problems of super high-rise building construction.

How tall can a building be called a "super high-rise building"? There is no clear stipulation in China's building code. China's Code for Fire Protection Design of High-rise Civil Buildings (GB50045-200 1 Edition) only specifies residential buildings with 10 floors or above, or public buildings with a height exceeding 24m, which are called "high-rise civil buildings". As for "super high-rise building", there is no clear definition. This code only has special requirements for civil buildings with a height of more than 100m or more than 32 floors in terms of refuge floor, apron, fire water pressure, fire extinguishing facilities, positive pressure smoke exhaust and automatic fire alarm. According to this understanding, can 100m be used as the boundary between "super high-rise" and "high-rise"? I think it's appropriate. Judging from Japan's (fire protection law), its boundary for high-rise buildings is 3 1m high or 10-storey buildings. In a book published in Japan 1999, buildings with a height of more than 100m or more than 25 stories are further defined as "super high-rise buildings" with a height of more than 300m or? Buildings with more than 5 floors are called "super high-rise buildings". In fact, by 2000, the tallest building in Japan was only 296m high (a landmark building in Yokohama, with 70 floors above ground and 3 floors underground, built in 1993).

The construction of super high-rise buildings with a height of 100 meters in China began in the 1970s. The outstanding example at that time was baiyun hotel, Guangzhou, which was 1 15m high and 1976. In 1980s, after experiencing the catastrophe of the Cultural Revolution, China turned to the situation of reform and opening up. In order to meet the needs of economic development, a number of high-rise buildings over 100 meters have sprung up in coastal open areas. First of all, it is concentrated in Guangzhou and Shenzhen, and there are also some between Shanghai and Tianjin. It is not yet possible to form a climate. The real high-rise buildings appeared in the 1990s. Especially after 1992, the excellent situation of reform and opening up was further formed, and huge buildings stood on the land of the motherland. According to the statistics of China Institute of Building Science, by the end of 1996, among the tallest buildings in China, the lowest is 120m, and there are 8 buildings with a height exceeding 200m. By the end of 1998, among the tallest buildings in China, 100, the lowest is 150m, and there are 20 buildings over 300m, and the highest is 420m. Among them, Shenzhen Wang Di Building (322m, 8 1 floor, 1996) is a world-class high-rise building. 1996 completed, the world's 12 tallest building) and Shanghai Jinmao Tower (420.5m, 88th floor, 1998 completed, the world's third tallest building). This is enough to become a "super high-rise building". According to incomplete statistics, there are 46,660 high-rise buildings in China, and there are 850 super-high-rise buildings exceeding 100 meters.

In 2000, several places in China put forward plans to build super high-rise buildings. In Beijing alone, there are two high-rise buildings over 300m and three high-rise buildings over 500m.

In August, 2000, the first anniversary of the opening of Jinmao Tower, Shanghai held an international seminar on super high-rise building management, and invited the property managers of the four tallest buildings in the world, namely, Kuala Lumpur Twin Towers, Chicago Sears Tower, Shanghai Jinmao Tower and New York World Trade Center. Alan Reiss, the property manager of the World Trade Center in New York, introduced the management experience of the World Trade Center in New York in great detail, especially a series of measures taken to deal with emergencies after the 1993 terrorist car bomb attack. We listened at that time and admired their thoughtfulness. But what I didn't expect at that time was that just one year later, the "9. 1 1" incident razed the World Trade Center in New York. It is not known whether Mr. Reese was killed. The meeting also invited the heads of Yokohama Landmark Building, the tallest building in Japan, and Sanliu Building, the tallest building in Seoul, South Korea, to attend the meeting. The meeting was very successful, but it had little impact on the domestic construction industry.

Super-high-rise buildings are very expensive because of their huge volume, complex functions, large number of people and huge investment. Usually because of its special status, it becomes a landmark building in a region. In recent years, it is appropriate to call such buildings the concentrated expression of science and technology, the symbol of comprehensive national strength, the symbol of the city and so on. It really embodies many material achievements. It takes a lot of manpower, material resources and financial resources. The cost per square meter of Jinmao Tower is generally 20,000 RMB, and the daily normal operating expenses are about one million RMB. Therefore, the construction and maintenance of super high-rise buildings will consume a lot of wealth. As far as the huge maintenance cost of modern super-high-rise buildings is concerned, it has lost the significance of building such buildings in the early days to save land. According to the document published by DEGW in 1999, if the life cycle of a building is 65 years, the ratio of construction cost to maintenance cost is about 1: 3 to 1: 4. If the daily maintenance cost of Shanghai Jinmao Tower is1000000 yuan, the 65-year service life will be about 23.7 billion yuan.

First, turn ordinary problems into special problems.

From the perspective of civil engineering, there should be no technical problems in building super high-rise buildings. China has repeatedly proposed to build a building more than 500 meters, which shows that the technology is feasible. Someone said, "Technically, architecture? Kilometers high buildings are also possible. " But from the perspective of equipment and equipment system, it is not so simple. Super high-rise building is by no means an extension or simple superposition of ordinary buildings. General problems in general buildings have become special problems in super high-rise buildings, which need special attention and treatment. Among these problems, some problems will become more and more prominent in super high-rise buildings, and even some problems have become international intractable diseases.

There is no doubt that high-rise buildings have to withstand crosswinds. However, how much impact will it have on the building? Generally speaking, under normal wind pressure, the height from the ground is 10m. If the wind speed is 5m/s, the wind speed can reach 15m/s at the height of 90m. If it is as high as 300-400m, the wind will be stronger, that is, when the wind speed reaches more than 30m/s, the shaking of skyscrapers will be very intense. When it is windy in spring, the World Trade Center in New York usually shakes 6- 12 inches (15-30cm) from the center. Under the action of strong hurricane, the displacement can reach 3 feet (1m), and the maximum deviation is designed to be 4 feet (7.3m) under the maximum wind force. According to the reported data, the maximum deviation from the center of Sears Tower in Chicago can reach 6 feet (2 meters) in the case of strong wind. It is said that they can adjust it to 5 feet after installing a gyro balance device. According to the wind tunnel test, the vertex displacement of Shanghai Jinmao Tower can reach 0.9-1.2m. ..

For this kind of shaking of buildings, the experience of World Trade Center in New York is to consider its influence on elevators first. Elevator is regarded as the "lifeline" of super high-rise buildings. There are 246 elevators in the World Trade Center in New York. When the elevator is running at high speed, if the building shakes more than 6 inches, the cable of the elevator will be damaged due to uneven stress when it is loose, which will cause danger. Therefore, they specially designed an alarm system and a follow-up tracking mechanism of elevator wire rope, which can adjust the length of elevator wire rope and the stress at the joint in time.

Another phenomenon that ordinary houses don't appear is that when the temperature is low in winter (according to the data of new york World Center, the temperature is below -6 degrees Celsius), cold air from lower floors (especially the lobby on the first floor) and the basement will break into the elevator shaft, forming a strong airflow through stack effect, which makes the elevator unable to close. And it will bring some smells from the bottom up, such as the smell of the kitchen and the smell of oil smoke. At this time, if there is welding operation or gas leakage on the ground floor or basement, the fire source may be brought to the top floor with the airflow, which is extremely dangerous. At the same time, due to the small gap between the elevator car and the shaft wall, when the elevator is running, the friction of airflow will produce howling, which also appears in Jinmao Building. According to SOM design firm in the United States, which is very experienced in the design of super high-rise buildings, this is an international problem, and no good solution has been found yet.

Several super-high-rise buildings have experienced accidents such as power failure and running water. From the management point of view, it is very important to have a person who knows the overall situation and all the details of the system, in addition to making plans to prevent accidents and making backup systems. The management of Shanghai Jinmao Building once felt very sorry that no one had mastered more than 4000 valves in the building/KLOC-0.

Clean glass has also become a problem in managing these behemoths. The curtain wall of Jinmao Building is 8000 square meters. It is said that two window cleaners can clean all the windows once a year by working continuously. Moreover, due to the uneven shape of the building, there are many overhangs, and in some places there are more than 3 meters, so it is quite difficult to clean the glass.

The above examples only show that common problems that are not problems for ordinary houses or buildings have become problems in super-high-rise buildings, and even become marijuana. The reason is that it is particularly high and complex, which makes it unique in design, construction, management and maintenance, and every point should be taken seriously.

Second, fire fighting is the top priority.

At the Shanghai conference, the managers of six internationally famous buildings all raised one of the most important issues, that is, fire prevention. More consideration should be given to this and more preventive measures should be taken.

Super high-rise buildings usually have diverse functions and complex equipment. There are many factors that may cause fire, such as too many electrical equipment, improper maintenance, management and use; Poor fire management and smoking; Mechanical failure or improper construction operation. If natural disasters (lightning strikes) and man-made disasters (arson damage) are added, it can be said that the potential and possibility of fire is great. If we analyze the causes of the fire, although the hidden fire hazards and causes of ordinary houses are nothing more than these, once a fire is formed, its harm is greater than that of ordinary buildings. According to Shen Youdi, chief engineer of Shanghai Fire Bureau, there are mainly the following three aspects:

1, the fire spread rapidly. There are many combustible materials (decoration materials, furniture, articles, pipe insulation materials, wire sheaths) in the super high-rise building, and several vertical chimneys are formed in the vertical pipes and shafts of the super high-rise building. In case of fire, the effect of pulling wind and pulling force will promote the spread of flame and smoke. The higher the height, the greater the pulling force and the stronger the stack effect. In super high-rise buildings, the vertical rising speed of flue gas along stairwells or shafts is about 3-4m per second. A 100m building, if not blocked, can lead the fire to the top floor in half a minute. It should be said that this kind of "stack effect" is the most embarrassing and difficult to prevent for super high-rise buildings. Although fire dampers can be installed in some pipes, if the control fails or cannot be closed tightly, sometimes the fire may overflow and burn. In addition, the flame from the window extends to the next floor along the external wall, or sparks or flames are blown out by the wind, sometimes igniting other nearby buildings. The higher the building, the farther it may blow and the greater the harm.

It is difficult to evacuate the crowd. Super high-rise buildings, especially super high-rise buildings, often gather a large number of working and living people. For example, the Twin Towers of the World Trade Center in New York have 40,000 staff members and 6,000 visitors every day. Generally speaking, high-rise buildings over 300m can accommodate more than 1 10,000 people. In case of fire, except for the fire elevator, all passenger and cargo elevators must immediately descend to the ground floor and cannot be used. So a large number of people need to evacuate through the stairs. The higher the floor, the more people and the longer the evacuation time. Thousands of people have to walk down and out of buildings hundreds of meters high, and the time varies from tens of minutes to several hours. Moreover, this evacuation cannot rely on the fire ladder truck. First, the number is limited, not to mention these ladder trucks have to perform high-altitude combat tasks such as fire fighting; The other is that the height of the ladder truck is limited. China's code stipulates that the height of fire fighting aerial work is 24 meters, while the highest height of ladder trucks in Shanghai, Beijing and other big cities can only reach 33 meters.

It is difficult to put out the fire. When a fire breaks out in a super high-rise building, we often encounter specific difficulties such as narrow space around the building and limited climbing height. Therefore, even in the specification, it is listed that "high-rise buildings should be self-help because it is difficult to save from the outside". As mentioned above, the fire in high-rise buildings spreads very fast, which makes it very difficult to put out the fire. In addition, there are many unfavorable factors that hinder the battle. For example, a large area of glass curtain wall explodes outward under the internal high-temperature baking, and the glass rain formed by the splashing of glass fragments flies like a sword, which makes the external fire fighting team unable to get close. Another example is high-altitude fire fighting, insufficient water source or insufficient water pressure. For another example, in the absence of a dedicated fire elevator, firefighters can only climb by physical strength and need to be fully armed. Generally, people climb to the 8-9 floor, and the physical consumption can no longer maintain the normal fire fighting, which makes the fire fighting more difficult.

To sum up, tall buildings are afraid of fire. The higher the building, the bigger the hidden danger. Once a disaster is formed, its danger and the loss of people, money and things are incalculable. If you build a super high-rise, especially a super high-rise fire protection, you have to think carefully.

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